In all wireless communications, a variety of demands for interference control are present. However, in this document, a wireless local area network (WLAN) system is mainly described as an example of the system to which the present invention can be applied.
Standards for a Wireless Local Area Network (WLAN) technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. IEEE 802.11a and b use an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps for four spatial streams by applying Multiple Input Multiple Output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps.
The above-described WLAN standards have evolved into IEEE 802.11 ac that uses a bandwidth of up to 160 MHz and supports a transmission rate of up to 1 Gbits/s for 8 spatial streams and IEEE 802.11 ax standards are under discussion.
Since communication in IEEE 802.11 is performed through a shared wireless medium, it has characteristics fundamentally different from those of a wired channel environment. For instance, in a wired communication environment, communication was made possible based on CSMA/CD (carrier sense multiple access/collision detection). In particular, if a signal is transmitted once from a transmitting end, the signal may be transmitted to a receiving end without significant signal attenuation since there is almost no change in a channel environment. In this case, if two or more signals collide with each other, reception power detected by the receiving end becomes temporarily greater than power transmitted by the transmitting end. Thus, whether the collision occurs may be detected through the instantly increased reception power.
However, in a wireless channel environment, since various elements (e.g., depending on a distance, signal attenuation may be increased or be deep-faded instantly) affect a channel, a transmitting end cannot precisely perform carrier sensing regarding whether a signal has been properly received by a receiving end or whether a collision between signals has occurred.